At the present time—see for example U.S. Pat. No. 5,203,144—sheets of sheet material are fed to the wrapping means by a feed system comprising three operating members and various devices and, more particularly, from the upstream to the downstream end, sheet feed means, a first sheet conveyor and a second sheet conveyor, in which the said sheet feed means feed the sheets towards and on to the first sheet conveyor, in which the said two sheet conveyors are placed in sequence with respect to the direction of feed of the sheets, in which by means of the said various devices the first sheet conveyor, located upstream, is driven at a constant speed and the second sheet conveyor, located downstream, is driven at variable speed.
This known system carries out the function of feeding the sheets to the wrapper means very successfully, but gives rise to various problems.
A first problem is due to the fact that the system comprises a multiplicity of components, with consequent high production, maintenance and running costs.
A second problem is due to the fact that two phases of transfer are provided for each sheet, namely a first phase in which the sheet is transferred from the feed means to the first sheet conveyor and a second phase in which the sheet is transferred from the said first sheet conveyor to the said second sheet conveyor with consequent possible errors of misalignment of the longitudinal position of the sheet during the said transfers, in which the summation of two possible transfer errors could bring about an incorrect positioning of the sheet (in other words leading or lagging) with respect to the machine cycle of the advance of the objects and/or of the wrapping bars.